With the prosperous development of computer technology and the Internet, the use of cloud computing is becoming more and more popular. Due to the trend of cloud computing, data centers play a role more important than ever. Modern large-scale data center may include hundreds of thousands of physical machines, such as servers. Each of the physical machines may contain a plurality of virtual machines operating thereon. The tenants of the large-scale data center may rent the virtual machines to use cloud resource which is supplied by the large-scale data center for computing, retrieving, and storing data. It is generally considered that the network of the “large-scale data center” has the following features, including: (1) able to provide more than one hundred of thousands of physical machines and one million virtual machines; (2) able to allow the tenants to assign the private IP addresses of the virtual machines by themselves, so that the virtual machines of different tenants may designate repeated IP addresses; (3) able to promptly recover from malfunctioning; having the function of plug-and-plug (e.g., the network system may automatically set up the network settings of the network devices); (4) allowing flexible migration of virtual machines; (5) allowing the use of multiple tenants, wherein the tenants may set the VLAN by themselves; (6) having the ability of routing to dynamically balance the network loads; (7) able to detect the network topology and detect the virtual machines and the physical machines; and (8) capable of resolving network addresses and learning the addresses of media access control (MAC).
As the size of the large-scale data centers increases, the conventional network framework and technology can no longer satisfy the needs of the large-scale data centers. For a data center network framework based on a layer-3 (L3) network, there is a management issue of low flexibility and high complexity. For example, the assignment of IP addresses is limited by the framework of physical addresses and is rather inflexible in migration of virtual machines. Thus, recently, the configuration and operation of the conventional data center network have been developed based on the Ethernet switches of the layer-2 (L2) network.
However, for the framework of data center based on the L2 network, the issue of being difficult to enlarge the scale may arise. The framework of data center based on the L-2 network has difficulties in enlarging its scale for the following reasons. First, even though the spanning tree protocol (STP) may avoid the loop in the L2 network, multiple-path transmission (e.g., equal cost multi-path, ECMP) cannot be used. Also, the form size of the forwarding information base (FIB) of the Ethernet switches is limited, making the Ethernet switches frequently broadcast to look for the MAC address of the destination terminal of the packet. Besides, the Ethernet is not compatible with dynamic changes of routing and does not provide services guaranteeing the quality of service (QoS). In addition, the convergence time from malfunctioning for the Ethernet is too long. Lastly, the current IEEE 802.1Q standard can only provide 4096 virtual local area networks, and thus fails to meet the requirement on the number of tenants of the large-scale data center. Accordingly, how to design a data center network system that meets the requirements of the large-scale data centers is an issue that people having ordinary skills in the art should work on.